PROJECT SUMMARY This grant application, in response to PAR-14-284 ?High Throughput Screening (HTS) to Discover Chemical Probes?, proposes an outstanding collaborative effort between Mayo Clinic (Rochester, MN) and Sanford Burnham Prebys Medical Discovery Institute (SBP, Orlando, FL). Age-related organ fibrosis is a major cause for organ failure in humans and is accelerated in disease. Myocardial fibrosis, in particular, is a hallmark characteristic of the aged and diseased heart, and is a significant contributor to pathogenesis of heart failure (HF). Thus HF is thought of as the final cardiovascular aging pathway, of which is a major cause of morbidity, hospitalizations and mortality. However, effective therapeutic options are relatively non-existent to treat pathological fibrosis and HF, especially for our growing aging population. Research by our group and others, have firmly established that the particulate guanylyl cyclase B (pGC-B) receptor system mediates potent and pleiotropic anti-fibrotic effects through the generation of its second messenger, cGMP. Indeed, aging and HF studies have demonstrated that a deficiency of the pGC-B activator, CNP, resulted in elevated cardiac fibrosis and dysfunction, while therapeutic pGC-B activation via exogenous CNP-based peptides mediates a reduction in myocardial fibrosis and improved cardiac function. Together, this suggests that enhancing the pGC-B receptor system represents an unprecedented therapeutic opportunity for fibrotic disease, commonly seen in our elderly population, such as HF and beyond. To date, there are no small molecule drugs in existence to potentiate the pGC-B receptor and this proposal seeks to discover such novel therapeutic small molecules. We propose to identify small molecular enhancers (activators and/or positive allosteric modulators) targeting the pGC-B receptor by high throughput screening (HTS) of compounds from the NIH Molecular Libraries Small Molecule Repository. The Mayo Clinic investigators are internationally recognized for their extensive research on the biology, therapeutics and diagnostics of the pGC-B system in aging and disease, while the SBP team has a proven outstanding record of small molecule discovery by HTS. Our achievable studies will take advantage of the state-of-the-art HTS resources and drug discovery expertise of the SBP team and the translational and clinical expertise of the Mayo Clinic team. Studies to identify, validate and optimize pGC-B hits will performed at SBP and lead pGC-B enhancing hits will be functionally evaluated in human primary cell lines at Mayo Clinic. This innovative proposal is of high clinical impact as the drug discovery of a small molecule pGC-B enhancer, which currently does not exist, may have the potential of markedly reducing the burden of human age-related fibrosis and disease such as HF.